The present invention relates generally to apparatus for non-invasive monitoring of human physiological conditions, and more particularly to an ear canal pulse oximeter for monitoring the physiological conditions of pilots and other aircrew members flying high performance aircraft.
G-force induced loss of consciousness, or GLOC, is second only to spatial disorientation as a human factors threat to aircrew members of modern military high performance aircraft. GLOC is believed to be one of the primary causes of military aircrew fatalities notwithstanding the use of anti-G suits and other human factor improvements in modern military aircraft. Each improvement in aircraft performance since the early 1900's has been accompanied by an increased danger to aircrew members from human factors sources. Aircraft performance first reached a level sufficient to induce GLOC at least in the early 1920's, more than 65 years ago.
The U.S. Military, particularly the U.S. Air Force and U.S. Navy, has actively advanced the loss of consciousness prevention art. The Air Force and Navy are each the assignee of numerous patents in this art, including patents for reclined seats, advanced anti-G suits, rapid acting servo values for anti-G suits and G-limiting flight control computer systems, many of which are now standard equipment in modern high performance military aircraft. An example of such patents is U.S. Pat. No. 4,821,982 to Van Patten, which includes a discussion of the effect of acceleration and rate of change of acceleration on a pilot, and which patent is incorporated by reference in this application as though fully rewritten.
Notwithstanding these efforts, there has been a notable lack of satisfactory loss of consciousness monitoring devices for aircrew members. Such monitoring systems would monitor critical physiological factors, particularly blood oxygen saturation levels, and signal an alarm or actuate an automatic pilot system to assume control of the aircraft whenever monitored physiological factors fall to levels indicating imminent loss of consciousness.
The lack of such loss of consciousness monitoring devices is primarily because such monitoring has generally involved either anatomically invasive instrumentation devices or, at best, unwieldy external contrivances. These devices are, of course, highly disfavored or even considered physiologically and psychologically threatening by aircrew members, particularly fighter pilots.
To make such devices acceptable to aircrew members, they must be totally invisible in use or at least very unobtrusive. One useful approach to making such a device unobtrusive during use by aircrew members is described in copending commonly-assigned patent application Ser. No. 07/272,146, now U.S. Statutory Invention Registration H1039, "Intrusion-Free Physiological Condition Monitoring," by Tripp et al, which application is incorporated by reference in this application as though fully rewritten. That application discloses the modified use of a nasal septum probe, or oxisensor, used with a conventional medical pulse oximeter. The nasal septum probe fits over a patient's nose bridge, or septum. The nasal septum oxisensor is modified to mount within the nose bridge covering portion of a conventional aircrew member face mask so that the blood oxygen saturation and pulse rate of the aircrew member can be monitored without any noticeable interference with, or extra effort by, the aircrew member.
A pulse oximeter calculates blood oxygen saturation from the different rates at which oxygenated hemoglobin and reduced hemoglobin absorb light of different wavelengths or frequencies. Typically, two wavelengths of light are used, one in the red portion of the spectrum and the other in the infra-red. Also typically, absorption of the infra-red wavelengths is much less sensitive to blood oxygen saturation levels than is absorption of the red wavelengths, and the intensity of a particular infra-red wavelength remaining after passing through vascular tissue can serve as a constant against which to measure the intensity of a particular red wavelength remaining after passing through the same vascular tissue. Pulse rate is calculated from the timing of the relative rise and fall of the amount of light absorbed at each wavelength.
The pulse oximeter probe prior art has placed light emitting diodes (LEDs), and corresponding light sensors, over a variety of body appendages having sufficient vascular tissue. Such appendages include a finger, an ear pina, or ear lobe, the nasal septum as previously mentioned, and the scalp. The prior art frequently refers to ear oximeters, but in all cases it is referring to oximeters using probes, or oxisensors, that mount across the ear lobe.
A particular problem with adapting conventional medical monitoring devices for use on aircrew members while in active flight is maintaining accuracy. Conventional medical monitoring devices are generally attached in a hospital setting to a motionless and prone patient. Mounted on an aircrew member, they either will not remained attached or cannot maintain accuracy, or both.
Other than the invention described in the referenced copending commonly-assigned application, the prior art has not produced a successful means for monitoring blood oxygen saturation of aircrew members while in active flight.
A variety of different successful solutions to the problem of physiological monitoring of aircrew members will be necessary for persons working in the human factors field of art to chose from so that the most effective solution for each unique need will be available.
Thus it is seen that there is a need for additional physiological monitoring devices suitable for use with aircrew members during active flight.
It is, therefore, a principal object of the present invention to provide a non-invasive, unobtrusive physiological monitor for a pilot or aircrew member of a high performance aircraft.
It is another object of the present invention to provide a probe for a blood oxygen saturation level and pulse monitor that fits inside an ear canal.
It is a feature of the present invention that it can be incorporated as part of a protective ear plug already issued to aircrew members.
It is an advantage of the present invention that its placement inside a relatively dark body cavity greatly reduces its sensitivity to error from external light sources.
It is another advantage of the present invention that it measures blood oxygen saturation as near as possible to the area of primary concern, inside the brain of an aircrew member.
These and other objects, features and advantages of the present invention will become apparent as the description of certain representative embodiments proceeds.